* Greg KH - [http://driverdev.linuxdriverproject.org/pipermail/devel/2011-May/016658.html "At worse case, all of the code could go away and the normal logging interface be used, after it would be fixed up to handle the special needs that warrented the creation of the android logger code in the first place."]

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* Greg KH - [http://driverdev.linuxdriverproject.org/pipermail/devel/2011-May/016658.html "At worse case, all of the code could go away and the normal logging interface be used, after it would be fixed up to handle the special needs that warranted the creation of the android logger code in the first place."]

Android logger issues

This section describes some attributes of the Android logger code, which are
relevant for mainlining the code into Linux. Let's use a modified SWOT (Strengths,
Weaknesses, Opportunities, Threats) analysis for strategic planning to mainline
this code.

To find the logger's strengths and weaknesses, lets research and provide information
and hard numbers for how it compares with existing logging alternatives.

Alternatives

What are the alternatives to the Android logger?

logbuf (the kernel log buffer)

apparently, systemd uses

syslog

"the journal" - a new logging system for systemd (by Lennart Poettering)

One change, to add 'system' channel in Android, in last 3 years. System channel separates system log messages from application log messages to prevent buffer exhaustion in case of a chatty application.

Extension questions

Here are some questions about how the systems could be integrated:

What features could each log system have, if extended?

Would extension to an existing system interfere with it's current primary purpose?

For each change contemplated, can it be implemented to minimize the impact to existing code?

Barriers to entry as is (Weaknesses)

Does logger duplicate functionality that exists elsewhere?
Does it make sense to extend an existing system, rather than implement a new system?

What are barriers to entry:

use of ioctl?

hardcoded number of log channels

other style issues?

longterm maintainer?

Attractive features of logger as is (Strengths)

What are the differentiating features of logger, compared to alternatives?

minimal context switches for logging

use of ring buffer automatically limits log size

log is in memory (no cost to store unused log messages)

all messages are tagged

all messages have priority

all messages have timestamp

user-space program to filter messages by tag

channel selection by user-space policy

Discussions

This section has notes about discussions with the community kernel developers and with Google engineers,
with regards to mainlining this code

Google engineer requests/questions

Google doesn't want to change their class libraries or debug system

These have already shipped to developers and are integrated into other tools (eclipse log viewer)

the Android system and over 200,000 applications already use the existing classes

(So, can changes be made "under the hood" without changing the existing user interface?)

Google requests that any changes submitted to mainline also be placed in their kernel repository (or Gerrit review queue), so they can see them when they do merges and are not caught off guard.

I'm not sure the detailed steps required to perform this

Question: Why did Google write their own code, instead of using syslog?

Was it simply expedience, lack of familiarity with syslog, or are there specific reasons they wrote a new system (missing features, etc.)?

Logbuf and logger don't require writeable file system access which is mandatory for syslog. A no-writeable files-system (or a file-system which allow only few writes) is a common situation in embedded world.